Cisco DNCS System Release 2.7 3.7 4.2 설치 가이드
78-4011510-01 Rev C
DBDS System Time Overview
1-3
DBDS System Time Synchronization Overview,
Continued
DNCS (Solaris) Internal Clock
The DNCS maintains an offset from GMT based on the /etc/TIMEZONE file
The DNCS maintains an offset from GMT based on the /etc/TIMEZONE file
settings.
The DNCS broadcasts GMT system time messages (STMs) every 10 seconds to all
The DNCS broadcasts GMT system time messages (STMs) every 10 seconds to all
Digital Home Communications Terminals (DHCTs). These STMs, in conjunction
with the provisioned timezone settings, govern the time that is displayed on the
front panel of the DHCTs.
The QAM devices insert time into the Entitlement Control Messages (ECMs) it
The QAM devices insert time into the Entitlement Control Messages (ECMs) it
generates. The DHCT then validates this time against the time delivered in time-of-
day (TOD) Global Broadcast Authenticated Messages (GBAMs). This ECM/GBAM
time is only used for conditional access purposes and does not affect the time
displayed on the DHCT front panel.
External Global Positioning System (GPS) Clocks
With the GPS clock, the DNCS acquires its time synchronization using a signal from
External Global Positioning System (GPS) Clocks
With the GPS clock, the DNCS acquires its time synchronization using a signal from
the GPS satellite network. This is a highly accurate method of keeping time and has
the significant advantage of not depending on any other network devices to
maintain correct time on the DNCS. There is a simple, direct connection between the
GPS receiver and the DNCS. This connection is described in further detail in Chapter
2 of this document.
NTP Server Sites
NTP servers are an alternative to using the GPS for time synchronization. If a site is
NTP Server Sites
NTP servers are an alternative to using the GPS for time synchronization. If a site is
unable to use the GPS, they may elect to use an NTP server. NTP servers are located
throughout the world and are accessible using the Internet.
In an NTP server configuration, the DNCS receives its time from an NTP server. This
In an NTP server configuration, the DNCS receives its time from an NTP server. This
is as accurate as the GPS-based solution. The only drawback to using an NTP server
is that the DNCS must have a reliable network connection to keep the system time
accurate and up to date. The NTP server option has some added configuration
complexity and the opportunity for a failure is increased. NTP server configuration
is discussed in further detail in Chapter 3 of this document.